1. Field of the Invention
This invention relates to an apparatus which selectively applies agricultural liquid chemicals to plants.
2. Description of the Prior Art
In the prior art the literature teaches that herbicides are applied as sprays, in water or oil, or as dry granules. Basically, herbicides are applied by spraying over the top of plants or directed under the plant canopy toward the base of crop plants. When herbicides are sprayed on the soil before planting or emergence of crop plants, they may be either left on the soil surface or physically incorporated into the soil. Their characteristic phytotoxic properties may be altered by surfactant such as sticking and wetting agents added to their formulations or spray solutions, or by the kind of formulation used, such as granular formulation in place of an emulsifiable concentrate. Other techniques are known but seldom used in the art of applying herbicides. These include the injection of liquid or gaseous formulations directly into the soil with or without the use of an impervious shield, such as a plastic sheet to retain the vapors in the soil, and the use of bars of wax containing the herbicide to rub over the tops of plants. Phenoxy herbicides have been applied to weeds growing above crops by wrapping a tractor-mounted spray-boom with burlap or some other absorbent material. The limiting factor with this concept was to keep the absorbent material sufficiently wet, but avoid dripping the herbicide onto the crop. Herbicides have been sprayed to weeds above the crop canopy with a recirculating sprayer. This system sprays a herbicide solution across the crop row and any herbicide not retained by the weeds is collected by a large spray trap. With this system some herbicide spray may ricochet from the weeds onto crop plants, and some drift of fine spray particles may cause crop injury. With prolonged use of the recirculating sprayer, dirt and plant debris accumulate in the spray traps and ultimately, in the herbicide solution. The debris is troublesome because it impedes the flow of herbicide solution through the strainers and nozzles and will ultimately inactivate the herbicide. The rope wick applicator was developed to apply herbicides to weeds taller than the crop. This system requires no pumps or moving parts to deliver the herbicide. It is simply drawn from the reservoir by capillary action and then rubbed on weeds contacting the rope as the applicator moves across the field. With the rope wick applicator the volume of liquid delivered through the rope without drippage is limited to a very narrow range. Under enviornmental conditions of low humidity, high temperatures, or brisk wind, the ropes dry very rapidly. To obtain acceptable control relatively slow speeds of application must be maintained and because the ropes wet only one side of the weed, repeated trips through the field are often necessary.